1. Field of the Invention
The present invention relates to impact printers wherein the print member is moved relative to the printing medium and impact printing is carried out at a plurality of print positions along a lateral line on said printing medium by moving said print member so that a selected type character on said print member coincides with a particular print position and then impacting said character against said print medium through a suitable ink release ribbon or sheet.
2. Background and Prior Art
In the impact printer field, there has been an ever-increasing demand for higher and higher printing speeds in excess of 50 characters per second. In accordance with the present state of the art, printers which utilize rotating disks with characters arranged on the periphery thereof have been extensively used commercially. These printers generally fall into the daisy wheel class of printers in which print elements have a plurality of type characters respectively arranged mounted at the ends of a corresponding plurality of spokes or petals extending from a central hub. U.S. Pat. Nos. 4,178,108, 4,189,246, 3,858,509 and 4,044,880 are directed to impact printers using such print wheels. Printers of this type are presently in use with considerable commercial success.
However, this group of impact printers appears to have upper limitations in print speed. It is believed that current daisy wheel impact printers have upper speed limitations in the order of 90-100 cps.
In order to achieve high speed impact printing in excess of 100 cps, the present invention, in effect provides a new technology in impact printers by providing print members having a plurality of interspaced small diameter helices.
In this connection, it should be noted that print elements utilizing a plurality of discrete helices are known in the impact printer art. U.S. Pat. No. 3,724,631, "Printer with Helically Arranged Type Divided into Axially Offset Group," S. L. Kaczeus, issued Apr. 3, 1973 and U.S. Pat. No. 4,138,942, "Printing Device for Printing on a Continuously Moving Form," R. Hutley, issued Feb. 13, 1979. Each disclose print members comprising a plurality of helical elements each having a font of type characters peripherally arranged thereupon. However, in the structures of this prior art, no two of the helices are interspaced with each other, and consequently as will be set forth hereinafter in greater detail, it is not possible to structure helical elements in the patented apparatus into small radius and consequently low inertia print elements.